I'm trying to put together a smart campaign that automatically fills in the date of when an action is triggered (like opening an email) but only if that date is empty. So if someone opens an email, it will trigger the flow: "If opt in date is empty, opt in date is today." If I choose today, will it keep the date that I chose or will it update the date based on when the action took place? I don't want to add in a specific date, I want it to be the date that the action occured.